This invention, in one of its aspects, relates to systems for maintaining alignment-sensitive aircraft-borne avionics and weapons sensors in precise alignment. In another aspect the invention relates to a method for precisely aligning any sensitive avionics or weapons system instrument which is subject to vibrations causing detrimental misalignment.
A problem faced by designers of advanced electronic military equipment is the strigent angular alignment requirement of aircraft avionics and weapon system sensors. Sensors such as Inertial Navigation Systems (INS), radar, forward looking infrared sensors (FLIR), head up displays, guns, and missile pylons all require precise alignment of the system sensitive axis. Sensor misalignments result directly in errors in navigation, target tracking, weapon delivery, and the like.
Meeting the alignment requirements in the case of advanced systems presents an ever-increasing problem. In airborne systems, as the alignment requirements of its sensors are becoming more stringent, advanced aircraft are becoming more flexible structurally. This means that ground-based boresighting procedures are too limited, and, therefore, no longer adequate. It also means that aircraft flexure effects must be taken into account during alignment. Because aircraft structural flexure is highly dependent on the aircraft's inflight conditions, some form of inflight alignment technique is required which provides for flexure angle compensation.
The former approach of designers of aircraft systems to the alignment requirement was to mechanically align each vibration sensitive sensor to a specified aircraft body-axis system. This approach required the use of precision machined surfaces, pins, slots, guide rails, and the like, in an attempt to achieve a specified alignment accuracy at the time of installation. It further required the capability of making precision adjustments, such as using shims or other means, in response to precise optical boresight measurements. Often a series of measure/adjust cycles is required to achieve the desired accuracy. Also, the desired alignment is often sensitive to variables which lead to alignment instability, such as the amount of torque applied to mounting lugs, mechanical creep due to age, landing shocks, temperature changes, and so forth.
Conventional sensor alignment systems are expensive and utilize complex optical-mechanical equipment and procedures, for instance aircraft jacks, optical targeting boards, precision optical mirrors, sophisticated tooling, and ground support personnel. Alignment accuracies deteriorate rapidly as the geometric complexity and separation distance between sensors to be aligned increase. Hence, in addition to being part of an aircraft's routine maintenance schedule, sensor alignment is required whenever an aircraft exceeds maneuver limits or when other general maintenance requires the removal of sensor subsystems.
As indicated, alignment requires considerable skill, sophisticated ground support equipment and time. Past alignment procedures also require ground personnel having the same skill level as those in the aircraft in order to operate such equipment as optical target boards, precision optical mirrors, autocollimators and other instruments. For example, consider the case of adjusting the jacks to simulate the aircraft's inflight orientation at one g for a specified aerodynamic condition. When the jacks are removed, the aircraft resumes an on-the-ground orientation which is often quite different from that with the jacks in place. This difference is associated with the aircraft's sensitivity to the way it is supported, that is, whether it is statically supported on the ground by its wheels, or dynamically supported in flight by its wings. This sensitivity to aircraft flexure under the differing one-g conditions is evidence of the flexure effect at the varying g levels. In addition aerodynamic conditions encountered in combat must be accounted for in the alignment process.
By the practice of this invention a system for aligning avionic/weapon sensors is provided which eliminates the need for support equipment outside the vehicle to boresight and align sensors on the the vehicle. It also allows more flexibility in the location of alignment-sensitive equipment when the vehicle, especially aircraft, is designed.